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SCSI. Chapter 13. SCSI. Small Computer System Interface introduced in 1979 as a means of mass storage Common SCSI devices Hard drives - Scanners Tape backup units - CD-ROM drives Removable hard drives - Printers. SCSI.

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slide1

SCSI

Chapter 13

slide2
SCSI

Small Computer System Interface

    • introduced in 1979 as a means of mass storage
  • Common SCSI devices
    • Hard drives - Scanners
    • Tape backup units - CD-ROM drives
    • Removable hard drives - Printers
slide3
SCSI
  • SCSI manifests itself through a SCSI chain, which is a series of SCSI devices working together through a host adapter
  • Host adapter attaches to the PC
    • picture on page 866
scsi chains
SCSI Chains
  • All SCSI devices can de divided into 2 groups: external and internal
  • External devices stand alone and hooked to the external connector of the host adapter
  • Internal devices attach to the host adapter internally and the devices sit in the PC
  • SCSI has 50-pin, 68-pin, or 80-pin cables
scsi chains1
SCSI Chains
  • If the SCI cables are plugged in incorrectly, they can damage the devices
  • External devices all have 2 connections in the back, which enable you to daisy-chain
  • SCSI can have a maximum of 8 (the host plus 7 others) or 16 (host + 15) depending on the SCSI chain
scsi ids
SCSI IDs
  • The values of the ID numbers range from 0 to 7, or 0 to 15
  • No 2 devices can share the same ID number
  • Host adapter is usually set to 7
  • Doesn’t matter what ID # other devices are set to
  • Try to use ID #0 for bootable hard drive
  • You can set SCSI IDs by setting jumpers
scsi chains2
SCSI chains
  • Each end of the chain must be terminated
    • examples of termination on page 877
  • some devices self-terminate, but others you have to do yourself
  • usually set with jumpers; sometimes switches
  • can damage devices if terminating improperly
scsi flavors
SCSI Flavors
  • Types of SCSI:
    • SCSI - 1: 8-bit
    • SCSI - 2: 8-bit
    • SCSI - 2: 16-bit (wide)
    • SCSI - 2: 32-bit (wide)
    • SCSI - 3: numerous
  • Refer to chart on page 884 for types
bus mastering
Bus mastering
  • Why is bus mastering an important part of SCSI?
    • devices that are on a SCSI chain can communicate with each other with very little use of the CPU, which frees up the system resources
scsi cable and connectors
SCSI Cable and connectors
  • SCSI-1 & SCSI-2 (8-bit) used Type A: 50 pins
  • SCSI-2 (16-bit) used Type B: 68 pins
  • Some of the higher end SCSI-3 cables use 80 pins
slide11
ASPI
  • Advanced SCSI programmer interface
    • mandates a standard way to write BIOS device drivers for SCSI devices
    • you can install a standardized set of device drivers for all your SCSI devices
compatibility with ide
Compatibility with IDE
  • IDE and SCSI can both exist in one machine
  • IDE will get priority for the boot drive; you should use CMOS setup which allows SCSI to take priority
  • Not a good idea to mix them
slide13
SCSI
  • SCSI adapters need an IRQ and usually take 3, so be careful with conflicts with COM ports.
    • Usually only happens with legacy PCs
  • Read the cost and benefits section on 893
scsi vs ide
SCSI vs. IDE
  • SCSI used to be much bigger, now the advantage is disappearing
  • SCSI is much faster, uses bus mastering, and can support up to 15 devices now but also more expensive